The present invention generally relates to semiconductor devices and more particularly to a film forming method of an insulation film suitable for production of ultra-miniaturized high-speed semiconductor devices.
With the progress in the art of device miniaturization, it is becoming possible in ultra high-speed semiconductor devices of these days to realize a semiconductor device having a gate length of 0.1 μm or less.
Generally, operational speed of a semiconductor device is improved with device miniaturization, while with such highly miniaturized semiconductor devices, there is a need of reducing the film thickness of the gate insulation film in accordance with scaling law with decrease of the gate length.
On the other hand, when the gate length has become 0.1 μm or less, it becomes necessary to set the thickness of the gate insulation film to 1-2 nm in the case a conventional thermal oxide film is used for the gate insulation film. With such a very thin gate insulation film, however, there occurs an increase of tunneling current, and it is not possible to avoid the problem of increase of the gate leakage current.
In the case of forming a gate insulation film with such a high-K dielectric material, it is preferable to form a silicon oxide film or silicon oxynitride film at the interface between the silicon substrate and the gate insulation film as the interface film with a film thickness of preferably 0.4 nm. Reference should be made to WO03/049173 official gazette, for example.
With the technology of WO03/049173, it becomes possible to form a high-quality insulation film on the silicon substrate surface at a low temperature of 450° C. or less, with a film thickness of about 0.4 nm in the case of a silicon oxide film or with the film thickness of about 0.5 nm in the case of a silicon oxynitride film.
However, in the case attempt has been made to form an oxide film or oxynitride film of the thickness of 0.4-0.5 nm at the temperature that exceeds 450° C., on the other hand, there arise various problems as will be explained below.
Conventionally, it has been practiced, when a silicon substrate is introduced into a processing vessel of a deposition apparatus as a substrate to be processed, to hold the substrate in the processing vessel in an oxygen gas atmosphere until a predetermined processing temperature is reached. Thereby, the problem of formation of projections and depressions on the substrate surface due to the etching reaction of volatile SiO, which may be formed when the substrate to be processed is held in an atmosphere of extremely low oxygen partial pressure as a result of the reaction caused between residual oxygen remaining in the atmosphere with extremely small amount and silicon on the substrate surface (M. Offenberg, J. Vac. Sci. Technol. A9, pp. 1058, 1991), is avoided.
However, when an oxidizing atmosphere is used in the temperature elevating step at the beginning phase of film formation, there arises a problem in that an oxide film having a thickness reaching 1 nm is formed already on the substrate surface at the time of starting the desired film forming process, in the event the film formation is to be made at the temperature of about 900° C. In the case of forming a gate insulation film, in particular, such increase of film thickness causes an increase in the lower limit thickness of the gate insulation film, thus imposing limitations to the improvement of operational speed in miniaturized semiconductor devices attained by decrease of the gate length. Particularly, in the case the insulation film thus formed is used for an interface film and a high-K dielectric gate insulation film is to be formed by forming a high-K dielectric film on such an interface film, the effect of decreasing the oxide film equivalent thickness attained by using such a high-K dielectric film is cancelled out.
In the case the initial temperature elevating step is carried out under a non-oxidizing atmosphere such that there is formed no oxide film, on the other hand, it is known that there arises a problem, in addition to the foregoing problem of formation of projections and depressions, in that the organic substance, contained in the air and adhered to the silicon substrate surface, forms SiC with elevation of temperature, by causing reaction with silicon on the substrate surface. Reference should be made for example to WO03/063220 or Kawase, et al., Technical Report of IEICE, SDM 2002-189, (2002-10).
When there is formed an insulation film such as oxide film on the substrate surface where SiC is formed, there is caused a tunneling leakage current in view of small bandgap of SiC, leading to the problem of remarkable increase of leakage current of the insulation film.